This application relates to a trailer slider failsafe mechanism for ensuring the slider locking pins are properly engaged prior to the release of the parking brakes.
Heavy combination vehicles include a tractor and one or more trailers. As known, trailers often incorporate a slider, which includes a pair of axles, the suspension and an apparatus for adjusting and locking the position of the slider along the length of the trailer. Typically, a linkage is actuated and locking pins are moved to engage selected holes in the frame rails of the trailer. With the locking pins removed from the holes, the slider position may be adjusted along the length of the frame rails. Once the slider reaches a new desired position, the actuation element is operated and the locking pins are moved into the holes in the trailer frame.
One challenge with the use of a slider, is to ensure the locking pins are engaged in the holes before the tractor begins to pull the trailer. If the locking pins are not fully engaged, then it is possible for the slider to move relative to the trailer, such as under hard braking or high acceleration. This would be undesirable.
Various proposals have been made in the prior art for systems that interlock the parking brake to the locking pin position. In these systems, if the locking pins are not engaged, then a valve will be in a position preventing flow of pressurized air to the parking brake control valve. As is known, vehicle parking brakes typically include a large spring that moves to set the brake, preventing movement of the trailer. With the parking brakes set, the trailer cannot move. Thus, these prior art systems are intended to prevent the trailer from moving unless the locking pins are engaged.
Trailers are equipped with an air supply line that is used to charge the trailer air reservoir and to retract the parking brakes. For modern North American trailers, a parking brake control valve is provided that usually directs air preferentially to the parking brakes and then to the reservoir. This valve also prevents loss of reservoir pressure if the supply line is disconnected. The reservoir supplies pressurized air to operate the service brakes and is also used for various other applications on the trailer. The prior art has proposed that the pin interlock valve should vent the supply line coming from the tractor and block any flow at the inlet to the parking brake control valve. Thus, in these prior art proposals, when the interlock valve vents the supply of pressurized air, the reservoir will not charge.
Moreover, in many modern systems, blocking the inlet to the parking brake control valve may actually lock the parking brakes in a release position if they are already released prior to the locking pins moving out of engagement. That is, if the parking brakes are released, and for whatever reason the pins are then withdrawn, the parking brakes cannot be set, and would stay in the release position. That is, with the valve in the prior art position, when the valve opens to vent the flow of air from the pressurized air supply line, it would block the line leading to the parking brake control valve. This could potentially lock the air already in the parking brake chamber, holding the brake away from its parked position.
Another problem with this prior art, is that if the reservoir is not charged and the supply line is vented, there may not be air to drive accessories. Many of the locking pin drives are pneumatically powered. In the absence of pressurized air in the reservoir, these systems would not be able to move the locking pins.